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Is this of interest to anyone? I won't be going (not in town) but it is free to attend, although you have to register in advance.

Solar Time Keeping

About this event

The motion of the sun through the heavens regulated the lives of early man. Various devices and systems for telling the hours have been adopted over the centuries. Even after the development of mechanical clocks the sundial was in regular use as a reference. Today sundials tend to be architectural adornments combining art & science. High profile events such as the Queen’s Jubilee and the Olympics regularly generate commissions for new and ever more imaginative designs.

About the speaker

Mike Groom is a power plant process engineer and a member of the IET. He has also had a long time interest in the history of astronomy and in particular time keeping and navigation. He is a member of the British Sundial Society, a learned society whose members include many designers and craftsmen. These members are responsible for most of the iconic sundials that grace a good number of public & private buildings around the country and overseas.
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io9 has an intriguing story about a planet larger than Earth and as dense as lead. (Not to mention being white hot).

A bit of digging turns up the paper that this story is based on, made available last week. However, in the course of searching for it I found this paper by another team, which whilst referencing the first paper (I assume they saw a draft) uses IR rather than optical measurements to come up with a diameter for 55 Cancri e that is half as much again as that derived in the other paper. That cuts the density dramatically for the same mass (which is fairly well-characterised) thus taking the planet from 'twice as dense as Mercury' to 'about as dense as Mars', which is a little less dramatic.

What both papers make clear, and which the io9 story doesn't, is that even if 55 Cancri e is as dense as lead, it isn't made of lead. Or comparably-dense silver or thorium, or even, alas, iron with a core of platinum. Rather, it's made of iron, but iron compressed to much greater than normal density by the sheer mass of the planet, some eight times that of Earth. Incidentally, a planet that close to its star couldn't be made of lead - at over 2,000 degrees, it would have boiled away...

So, be a little wary of dramatic science claims. It may be that someone has missed another paper, or just picked the one with the more dramatic conclusions.
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As promised, some notes from last night's IET Kelvin Lecture by Prof Pendry on invisibility.

We all know that light refracts when it enters a different medium from the one it was previously passing through. How much it refracts depends on a factor called the refractive index, which itself depends on two attributes of the material, its permittivity, or degree of interaction with electric fields, and its permeability, or degree of interaction with magnetic fields.

If you vary the permittivity and permeability of a material throughout a piece of it then you will have a material with an internally varying refractive index, which means that a ray of light travelling through it will curve. Now, since these properties depend mainly on the atomic structure of a material, you might think this would be difficult. But it turns out that you can fabricate lots of what are in effect tiny little electrical circuits, each of which acts like a small piece of material with adjustable permittivity and permeability. A lot of these together form a 'metamaterial' with tailored electromagnetic properties.

What you can in effect do is design a lump of metamaterial with a hole in the middle but which rays of light pass through in such a way as to bend around the hole and smoothly line up again. This makes the hole, and anything inside it, invisible. The model used is to take a spherical volume and consider a smaller sphere within it. The inner sphere is mathematically transformed to a point, a line, or (more practically) a flat sheet.

So far doing this at optical wavelengths is not possible, but it has been done with microwaves. In that picture, the gap between the white block (in effect a microwave mirror) and the yellow metamaterial is the cloaked space. Microwaves bounce off the white block as if the gap, or anything in it, wasn't there.

The clever bit is to take the required mathematical transform used to open up the hole, and to use it to calculate the required pattern of varying permittivity and permeability of the metamaterial elements.

Other things you can do with metamaterials include making materials with a negative refractive index, which never happens in nature. These have very odd optical properties, such as focussing with theoretically infinite resolution (a 'superlens').

Pendry gave an interesting example of what negative refractive index material would look like. If you look at a milk bottle, you don't see an inner volume of milk with a clear layer of glass around it; the milk seems to fill the glass, because any light refracted into the glass ends up being refracted further into the milk. If the bottle was made of negative refractive index glass, the milk would appear to extend beyond the bottle! Similarly, if you could give water a negative refractive index, objects under the surface would look as if they were hovering above it.

My own thoughts: In SF 'cloaking device' terms, you don't want to have to embed your spaceship in a large lump of transparent metamaterial! But if you have the sort of technology that could locally change the permittivity and permeability of free space in a nonlinear manner, then presumably you would achieve the same effect and could bend light around yourself. However, turning the cloak on would not make you fade to invisibility; rather, your ship would seem to shrink to a point or flatten itself to a plane (which Pendry suggested would look like a mirror, but a mirror is hard to see in dark space).

Thanks to [ profile] cthulie and [ profile] cdave for coming along, and to the former for suggesting the very nice Lyceum Tavern to retire to afterwards - somewhere I must have walked past dozens of times, but have never been in.
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Anyone else interested in attending this free lecture in London on Thursday 12th March (the week after the Tun)?

(There's a dinner afterwards, but its optional and not at all free, so I was thinking of heading elsewhere for nosh or drink if anyone else comes along).

Thursday, 12 March 2009
Savoy Place, London, UK
6.30pm (registration at 6.00pm)
6.00 pm Registration and Refreshments
6.30 pm The Centenary Kelvin Lecture (Chairman: Chris Earnshaw, President, The IET)

Creating the invisibility cloak: New horizons in electromagnetism

Electromagnetism encompasses much of modern technology. Its influence rests on our ability to deploy materials that can control the component electric and magnetic fields. A new class of materials has created some extraordinary possibilities such as a negative refractive index, and lenses whose resolution is limited only by the precision with which we can manufacture them.

Cloaks have been designed and built that hide objects within them, but remain completely invisible to external observers. The new materials, named metamaterials, have properties determined as much by their internal physical structure as by their chemical composition. The structure must be on a scale much less than the wavelength so that their responses can be described by an electrical permittivity and magnetic permeability.
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Is anyone else interested in attending this talk in London next Wednesday evening?

Conceptions of the Mind
Speaker: Professor Fairfid M. Caudle PhD, PhD, FIET, FRSA

Conceptions of the mind have fascinated humankind since prehistoric times and have come from diverse perspectives, including philosophy, psychology, physiology, engineering, and the visual arts. Explanations and depictions of the mind have often employed metaphors as tools to explore the location, organization, and dynamics of mental contents.

This illustrated lecture examines ways in which the mind has been conceptualised and represented. With regard to engineering, some metaphors have been influenced by technologies in place at the time, such as hydraulic systems, industrial machines, and, more recently, computers and transportation route maps.

Metaphors representing contents of the mind have been abundant in the visual arts. However, in neurophysiology and medicine, metaphors are increasingly being supplanted through ever more revealing images of the functioning brain

The talk is from 6.30-8 with refreshments beforehand and a reception afterwards. It's free, but you have to register online to attend.

The talk is at the Savoy Place, the London HQ of the Institution of Engineering and Technology (formerly the Institution of Electrical Engineers). It's at the north end of Waterloo Bridge, opposite Somerset House and close to Embankment and Temple tube stations.
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For the last couple of years I've been a subscriber to Pyramid, the on-line magazine of Steve Jackson Games. It's very much aimed at GMs (Game Masters, aka Keepers or Referees – the person who runs a role-playing game) with articles on scenario and character ideas, or discussions of the problems and opportunities that crop up when running RPGs. It's arguably worth the subscription for [ profile] princeofcairo's 'Suppressed Transmission' articles, but there's usually plenty of other stuff that captures my interest, often for reasons beyond just RPG-running.

The Jan 5th issue in particular had a very good article by Gregory Stauf exploring the reality behind the stereotype, familiar from any number of gaming genres or sf/crime TV shows, of a character rushing into a lab with the Unexplained Object of the day, saying "I need this analysed, right away!" – and more often than not, being told (in a remarkably short time) "It's utterly unknown to science!". As Stauf points out, not only is real-world scientific analysis a lot more complicated than that, but the whole issue is much more subtle.

Read more... )


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Simon Bradshaw

September 2017



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